In rotary machines, an electromagnetic induction voltage caused by magnetic imbalance and an electrostatic voltage resulting from rotational friction generate a shaft voltage in the shaft system. This shaft voltage causes current to flow in the shaft system and causes discharge at the bearing portions, which may cause electrolytic corrosion.
To secure the safety of rotary machines, it is necessary to prevent the electrolytic corrosion at the bearing portions resulting from the shaft voltage. In light of this, as a technique to keep the shaft voltage low enough by effective grounding, shaft grounding devices have been developed which discharge a shaft voltage generated in the shaft system by providing a shaft grounding brush to be in contact with the shaft system (for example, Patent Document 1).
The shaft grounding brush in such shaft grounding devices, in contact with the shaft system of the rotary machine, wears, and thus, the shaft grounding devices are attached on an end side of the rotary machine, being separated from the rotor and the like so that the wear of the shaft grounding brush does not affect the rotor and the like.